I don’t know about you, but all my tanks these days don’t have lids on them anymore. With the widespread use of frame-mount and pendant-mount lighting, heat reduction benefits, and better gas exchange, an uncovered marine tank is the way to go. But this also increases evaporation substantially. A small 60 gallon reef aquarium of mine loses almost a gallon of water per day. My 125 gallon FOWLR is almost twice that.
When I installed my first auto-topoff system 10 years ago, it had such a profound affect on my aquarium maintenance that I wound up adding 2 more tanks in my house. Not because the task of adding water manually was such a burden, but my tanks didn’t need me as often- and with adding top off water manually that’s at least every 24 hours. I could leave the house for a long weekend trip without having anyone watch my tanks. Likewise, there are often brutal days at work that in the evening, I don’t want to do anything but veg-out in front of the TV. The last thing I need to do is run around with jugs of RO water. It got to the point where when I walk passed my aquarium I don’t enjoy the view, but rather open the cabinet and check the sump mark to see if it needs water.
If there is any drudgery in the marine aquarium hobby, it’s got to be the task of adding top off water. Most people do this once a day. Waiting any longer or just forgetting to do it at all usually means adding a lot more freshwater and swinging the salinity a bit too much for the well being of your animals. LPS corals are very sensitive to abrupt salinity changes and can cause permanent tissue damage. Snails are really sensitive- they will die off en masse under moderate but quick changes in salinity.
Here’s a quick and dirty solution to the auto-topoff problem. It requires no electricity, float switches, or redundancy to prevent accidental overflows. It uses only gravity and buoyancy which, the last time I checked, doesn’t fail very often.
First step you need to purchase the Kent Marine Float Valve, model number #FVKENT. Don’t buy the whole kit with all the fittings. All you need is the valve only. These sell for around $20. The Kent float valve is basically an all-plastic toilet bowl float. What makes it nice is it has a height adjustment, so you can dial in exactly where you want the water level to be. It also uses ¼-inch poly line so any fittings and tubing sold for icemaker installations work. These can be had at Lowe’s and Home Depot.
You can mount the float valve in the sump or in the aquarium. The float is kind of ugly, so if you have a choice, go for the sump mount. For acrylic sumps, you need to drill a 5/8-inch hole about 2 inches above the water line. You don’t need to drain the sump for this. Just take a hole saw or plastic drill bit and drill the hole. If you’re worried about the plastic shavings falling into the sump, you can either scoop them out afterwards (they float) or use a piece of masking tape on the inside of the sump.
For glass sumps, you can drill and use the same method, but it’s easier to make a U-shaped bracket to hook over the edge of the tank. The best material to use is black ABS plastic. There are a lot of things made from this material. It is almost always black and very soft. You can almost make a mark in it with your fingernail. ABS also as a very low melting temperature so all you need is your kitchen stove to shape it any way you want.
Cut a piece of scrap wood about the width of the top plastic frame on your aquarium. Most of these are about 1-1/2 inches wide. Wave the piece of ABS plastic about 6-inches above a lit burner on your stove. A lot of people use this method to shape rigid airline tubing. Use the exact same method. The plastic will soften quickly, then just wrap it around the piece of wood to make a U bracket. Run it under cold water to harden the plastic. Once the bracket is complete, you need to drill a hole for the float valve and a two other holes at the top so you can add a couple of nylon screws for mounting. You can get nylon screws at any hardware store. First use a steel screw and turn it into the plastic holes so it cuts the plastic into threads. The nylon screws should then fit perfectly.
If you are not that good at doing DIY stuff, here’s an alternative. You probably have an old hang on filter or some other equipment you’re not using anymore. Take your Dremel tool and with the cutoff blade, cut out the hanger part of the filter and use it for the bracket. If you don’t have an old filter laying around, check the clearance bins at the big pet stores. You might find something you can improvise really cheap.
Making a water reservoir is easy. You can use just about any container, such as Rubbermaid tub or an old salt bucket. Drill a whole for a ½-inch bulkhead and mount it. Install a fitting in the bulkhead that converts ½-inch pvc pipe threads to ¼-inch poly line. Set the reservoir higher than the sump level then connect the reservoir to the back of the float valve with a piece of ¼-inch poly tubing. Fill the reservoir and you’re done!
